Method of injection molding a preform and apparatus for the same

ABSTRACT

An injection molding apparatus for a preform is disclosed, having an injection molding station (14) and a cooling and ejection station (16). In the injection molding station (14), neck cavity molds (60), injection core molds (50) and an injection cavity mold (42) are clamped and preforms (1) are injection molded. Thereafter, the injection cavity mold (42) is separated at a relatively high temperature. The preforms (1) are transferred to the cooling and ejection station (16) while being cooled by the injection core molds (50) and neck cavity molds (60). While the next preforms (1) are being injection molded in the injection molding station (14), in the cooling and ejection station (16) cooling of the preforms (1) continues. After cooling the preforms (1) to a temperature suitable for release, the injection core molds (50) are separated only through a stroke sufficient to allow a space to open between core pins (52) of the injection core molds 50 and the inner surface of the preforms (1). Thereafter the neck cavity molds (60) are separated and the preforms (1) are ejected. When the injection molding of the next preforms (1) in the injection molding station (14) is completed, a rotary wheel (30) is driven rotatingly in the opposite direction to the previous operation, and the injection core molds (50) and neck cavity molds (60) are interchanged between the two stations (14 and 16).

FIELD OF THE INVENTION

The present invention relates to a method of injection molding apreform, and apparatus for the same, which ensures an adequate coolingtime, but allows a reduction in the injection molding cycle time.

BACKGROUND OF THE INVENTION

To injection-mold a preform requires at least an injection cavity molddefining the outer surface of the preform, and an injection core molddefining the inner surface of the preform. Furthermore, after clampingthe injection cavity mold and injection core mold together and injectionmolding the preform, it is necessary to maintain the molds in theclamped state until the preform is cooled to a temperature at which thepreform can be released from the molds.

Conventionally, therefore, to ensure that the preform temperature issufficiently low for releasing has required the injection molding cycletime to be increased, and thus the productive efficiency to be impaired.The following are four factors concerned with longer cooling times.

(1) If for example the preform is released from the injection cavitymold and injection core mold and ejected by dropping, the preform mustbe cooled so that the temperature when the mold is separated issufficiently low that the preform is not deformed by contact with otherobjects.

(2) If the temperature when the preform is released from the mold ishigh, then when removing the injection core mold from the preform,deformation problems caused by the preform sticking to the core mold mayoccur.

(3) If the temperature when the preform is released from the mold ishigh, since there is no longer any member restraining the deformation ofthe preform after the preform has been released from the injection coremold, deformation problems due to thermal unevenness or thermalshrinking may occur and prevent the preform from meeting its designrequirements.

(4) If the cooling by the injection core mold is inadequate, the innerperiphery of the preform in particular may suffer crystallization as aresult of the inadequate cooling, and a preform with a non-transparentbody may be obtained.

In response to this, Japanese Patent Publication No. Hei 4-15721 (1992)and Japanese Patent Application Laid-Open No. Hei 3-140219 (1991)disclose a rotary injection molding apparatus having an injectionmolding station, a cooling station and an ejection station disposed inthis order at halting positions of an intermittent rotary transportmeans, in which a preform molded at the injection molding station istransported supported by a neck mold of the intermittent transport meanssuccessively to the cooling station and ejection station.

In such a rotary injection molding apparatus, it is not necessary toconsider factor (1) above, but inevitably factors (2) to (4) still causethe injection molding cycle time to increase.

Further, in the case of such a rotary injection molding apparatus, thecooling station requires a cooling pot and a cooling core, and since itis further necessary to provide a separate ejection station, the numberof stations increases, and more neck molds are required. Thus such aninjection molding apparatus leads to increased size and complexity ofthe apparatus, and a larger number of components.

Using such a rotary injection molding apparatus, to preventcrystallization of the thickest portion of the preform, that is to say,the neck, it is also possible to cool the neck with the neck mold.However, since the rotation is one-directional, to provide a coolingmedium to the neck mold involves the use of a rotary coupling, whichcomplicates the mechanism further.

Moreover, without extracting the injection core mold completely from thepreform, it is not possible to eject the preform in a conventionalinjection molding apparatus, and a rotary injection molding apparatus itis not possible to transport the preform from the injection moldingstation to the next stage. To extract the injection core mold completelyfrom the preform in this way involves a long extraction movement, andthis leads to the problem of a high overall height for the apparatus.

If, however, the preform is ejected before complete cooling in theinjection core mold and injection cavity mold (with the preformmaintained at a temperature to allow processing at the next stage), andpasses to a next stage where it is subjected to secondary processingsuch as blow-molding, the following problems may occur.

(A) Unless the internal pressure (pressure maintained for injection) issufficient, concavities are formed on the injection cavity mold side ofthe preform, and a preform with a uniform temperature distribution isnot obtained. Therefore, when this preform is blow-molded, a product ofuniform thickness may not be obtained.

(B) If the internal pressure (pressure maintained for injection) isexcessively increased, a pressure difference arises between a gateportion and the end of the preform (for example the neck portion), and aresidual stress becomes large in the high pressure preform bottomportion. As a result, the blow-molding process does not yield a productwith an even thickness distribution.

(C) When the preform is cooled through the injection core and theinjection cavity, as the cooling proceeds the preform shrinks, and comesaway from the injection cavity. The outer surface of the preform,therefore, has some portions in contact with the injection cavity andsome not, as a result of which there are variations in the cooling rate,and the temperature is not uniform. Therefore, when this preform isblow-molded, a product of uniform thickness is not obtained.

In the light of this, the present invention has as its object theprovision of a method of injection molding a preform, and apparatus forthe same, which ensures an adequate cooling time, but allows a reductionin the injection molding cycle time and an improvement in productiveefficiency.

Another object of the present invention is the provision of a method ofinjection molding a preform, and apparatus for the same in which even ifthe preform is released from the mold at a high temperature, there is notemperature variation, or deformation of the preform resulting fromsticking of the preform to the injection core mold.

A further object of the present invention is the provision of a methodof injection molding a preform, and apparatus for the same in whichwhile the injection cycle time is reduced, white crystallization causedby insufficient cooling is avoided.

A further object of the present invention is the provision of a methodof injection molding a preform, and apparatus for the same in whichwithout unduly increasing the injection maintenance pressure whileinjection molding the preform, a preform with low residual stress isobtained, and even if concavities occur, the preform can be ejected withreduced non-uniformities in temperature by reducing the dependence onthe injection cavity mold for cooling.

SUMMARY OF THE INVENTION

The method of the present invention comprises:

a step in an injection molding station of injection molding a preform inclamped molds including an injection cavity mold and injection core moldeach of which has a cooling portion;

a step in said injection molding station of releasing said preform fromsaid injection cavity mold;

a step of transferring said preform while being cooled by said injectioncore mold to a cooling and ejection station; and

a step in said cooling and ejection station of cooling said preform bysaid injection core mold until injection molding of a next preform insaid injection molding station is completed, and thereafter ejectingsaid preform from said injection core mold.

According to the method of the present invention, a preforminjection-molded in the injection molding station is cooled by theinjection cavity mold and injection core mold, and thereafter thepreform is released only from the injection cavity mold. Thereafter thepreform is transferred by means of the injection core mold to thecooling and ejection station. Both during the transfer and in thecooling and ejection station, the preform is cooled by the injectioncore mold, and thereafter the preform is ejected.

As a result, even after the injection cavity mold has been separatedfrom the preform in the injection molding station, since it is cooled bythe injection core mold, an adequate cooling time for the preform can beassured. This allows the injection cavity mold to be separated in theinjection molding station at a higher temperature, and shortens theinjection molding cycle time. Moreover, when with this highertemperature the injection cavity mold is separated, the injection coremold prevents deformation of the preform, and moreover crystallizationand non-transparency of the body of the preform caused by inadequatecooling can be prevented.

In said injection molding step, said preform, which has a neck portionhaving an undercut with respect to the direction of mold-opening, can beinjection molded using a neck cavity mold defining the outer surface ofsaid neck portion. This neck cavity mold comprises a split pair of moldshaving cooling portions.

When a neck cavity mold is used, in said transfer step and said coolingstep in said cooling and ejection station, said preform is cooled withsaid injection core mold and said neck cavity mold maintained in theclamped state. Moreover, in said ejection step in said cooling andejection station, said injection core mold is separated from said neckcavity mold by relative driving through only a stroke sufficient toallow a space to open between said injection core mold and the innersurface of said preform held by said neck cavity mold. Thereafter saidsplit pair of molds of said neck cavity mold is driven to be separated,and said preform is ejected.

In this case, even after separation of the injection core mold, the neckportion of the preform continues to be cooled by the neck cavity mold,the thick neck portion can be adequately cooled, and whitecrystallization thereof is prevented. Moreover, since there is nonecessity to withdraw the injection core mold from the entire length ofthe preform, the mold-opening stroke of the injection core mold can bereduced.

Moreover, since even after separation of the injection core mold, theinjection core mold remains within the preform, even if the preformshould adhere to either of the split pair of molds constituting the neckcavity mold, movement of the preform in the direction of driving saidpair of split molds to be separated is restricted by the injection coremold.

The cooling time of said preform can be adjusted by adjusting the timingof said mold-opening driving in said cooling and ejection station. As aresult, without necessarily changing the injection molding cycle time,the optimum cooling time for the preform can be ensured. Moreover, byadjusting the timing of separating the injection core mold, the increasein release pressure with the progress of cooling of the preform can bemet, and an injection molding apparatus of general applicability can beprovided.

It is preferable that said injection core mold and said neck cavity moldtogether are reversibly rotated between said injection molding stationand said cooling and ejection station, which being separated bysubstantially 180 degrees, and said injection core mold and said neckcavity mold are transferred so as to be interchanged between saidstations.

Reversing the direction of interchange of the injection core mold andneck cavity mold between the stations once per cycle simplifies theconnections of pipes circulating cooling medium to the injection coremold and neck cavity mold.

In said transfer step and during cooling in said cooling and ejectionstation, said neck cavity mold is held in contact with said injectioncore mold by a return spring, maintaining the clamped state of both saidmolds, as a result of which the clamped state of the molds can bemaintained without requiring a power source, and the cooling of thepreform can be promoted.

In this case, in said cooling and ejection station, said neck cavitymold holding said preform is pulled away from said injection core moldby an external force opposing the urging force of said return spring, sothat said injection core mold is separated from said preform.

It is preferable that the step of separating said injection cavity moldis carried out after the formation of a skin layer on the outer surfaceof said preform cooled by said injection cavity mold sufficient tomaintain the shape of said preform after separation from said injectioncavity mold. This prevents deformation of the preform after separationof the injection cavity mold, while enabling the minimum injectionmolding cycle time to be attained.

If the neck portion has no undercut, and it is not necessary to use aneck cavity mold, in said cooling and ejection station, said preform maybe ejected by blowing air from said injection core mold within saidpreform.

The method of blow molding of the present invention comprises:

a step of transferring a preform injection-molded as described above toa blow-molding station while the heat of injection molding is retained;and

a step of blow-molding a hollow body from said preform, by disposingsaid preform in a blow cavity mold, applying longitudinal stretching bymeans of a stretching rod, and introducing air from a blow core mold insaid blow-molding station.

In the case where the preform is to be released from the injection moldbefore cooling is complete, and subjected to secondary processing suchas blow-molding, since the preform is released from the injection cavitymold earlier, uniform cooling of the inner surface of the preform by theinjection core mold is obtained from the increased contact pressure dueto shrinkage of the preform, and therefore the quality of the productcan be significantly improved, and particularly the desired thicknessdistribution of the product resulting from the secondary processing suchas blow-molding, can be obtained.

The injection molding apparatus for a preform of the present inventionhas an injection molding station for injection molding a preform, and acooling and ejection station for releasing and ejecting said preformafter cooling, and comprising:

injection core molds disposed at positions corresponding to both of saidstations and having a function of cooling said preform;

an interchange transfer means for interchanging said injection coremolds between said both stations;

an injection cavity mold adapted to be clamped with said injection coremold disposed in said injection molding station, and having a functionof cooling said preform;

a mold clamping means operating to clamp said injection core mold andinjection cavity mold in said injection molding station, and alsooperating to separate relatively said injection cavity mold from saidpreform; and

an ejection means, operating to eject said preform from said injectioncore mold after said preform disposed in said cooling and ejectionstation has been cooled by said injection core mold.

By means of such an apparatus, the above-described method of the presentinvention can be practiced, and while reducing the injection moldingcycle time, adequate cooling time for the preform can be assured.

It is preferable that said interchange transfer means comprises a rotarywheel executing intermittent rotary transfer of said injection core moldbetween said injection molding station and cooling and ejection station,which being disposed at rotary positions separated by substantially 180degrees.

In the apparatus of the present invention, a neck cavity mold can beused. In this case, the neck cavity mold adapted to be clamped andopened relatively with said injection core mold is supported by saidrotary wheel. This neck cavity mold comprises a split pair of moldsdefining the outer surface of a neck portion of said preform, and saidsplit pair of molds each have cooling portions.

In this case, said rotary wheel transfers said preform having beeninjection molded to said cooling and ejection station while said preformis being cooled by said neck cavity mold and said injection core mold.

When using a neck cavity mold as described above, said ejection meanscomprises:

a mold opening means which operates to separate said neck cavity moldrelative to said injection core mold through only a stroke sufficient toallow a space to open between said injection core mold and the innersurface of said preform held by said neck cavity mold; and

a split mold opening means which after said neck cavity mold has beensubject to said relative mold opening operates to separate said splitpair of molds and eject said preform.

In order to maintain the injection core mold and neck cavity mold in theclamped state during transfer, a return spring is further provided,which urges said neck cavity mold against said injection core mold andmaintains both molds in the clamped state. Here, said mold opening meansopposes the urging force of said return spring and operates to separatesaid neck cavity mold relative to said injection core mold.

As a construction for supporting the neck cavity mold may be provided:

two split plates supporting respective of said split pair of moldsconstituting said neck cavity mold;

a guide member guidably supporting said two split plates so as to beselectively contacted or separated, and to which said return spring isattached;

a pressure plate disposed above said two split plates; and

a driven shaft erected in the upward direction above said pressure plateand of such a length that the upper end does not reach said rotarywheel.

In this case, said mold opening means comprises:

a through hole provided in said rotary wheel in a position correspondingto said driven shaft;

a drive shaft having a lower end above said through hole; and

a first drive means pressingly driving said drive shaft.

By the operation of said first drive means, the lower end of said driveshaft, having passed through and below said through hole in said rotarywheel, pressingly drives said driven shaft, and opposing the urgingforce of said return spring operates to separate said neck cavity moldfrom said injection core mold.

As a construction for mold opening of said split pair of moldsconstituting said neck cavity mold may be provided:

said two split plates may have wedge-shaped notch portions at opposingends; and

a vertically moving plate may be provided which moves verticallytogether with said drive shaft in response to operation of said firstdrive means.

Said split mold opening means may further comprise:

a second drive means mounted on said vertically moving plate; and

a cam plate driven downward by said second drive member, and having awedge-shaped end portion which engages with said notch portions formedin said two split plates.

In this way, after the vertically moving plate is driven downward toseparate the injection core mold, the cam plate is driven downward bysaid second drive member, and the lowering stroke of the cam plate canbe reduced.

It is preferable that the injection core mold, or said rotary wheel onwhich said injection core mold and the injection cavity mold aresupported is driven in a reciprocating rotary motion, reversing thedirection of rotary transfer for each operation. This simplifies thecirculation of cooling medium to the cooling portions of each of themolds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view showing one embodiment of the apparatusaccording to the present invention.

FIG. 2 is a bottom view of a rotary wheel.

FIG. 3 is a schematic perspective view showing a neck pressure platedriven downward.

FIG. 4A is a side elevation, showing the embodiment with the mold open,and FIG. 4B is a side elevation, showing the embodiment with the moldclamped.

FIG. 5 is a schematic sectional view showing the construction of theinjection core mold and neck cavity mold fitted on the rotary wheel.

FIG. 6 is a schematic diagram showing the mechanism for ejecting thepreform.

FIG. 7 is an enlarged sectional diagram of section A of FIG. 6.

FIG. 8 is a schematic diagram illustrating the open state of theinjection core mold.

FIG. 9 is a schematic diagram illustrating the ejection of a preform.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The method and apparatus of the present invention are now described interms of a preferred embodiment, with reference to FIGS. 1 to 9.

FIG. 1 is a schematic plan view of the embodiment, and in this figure,an injection unit 12 is disposed on a base 10, and in a positionopposing the injection unit 12 are provided adjacently an injectionmolding station 14 and a cooling and ejection station 16.

Below the injection molding station 14 is provided, as shown in FIGS. 4Aand 4B a lower mold clamping plate 20 fixed on the base 10. Above thislower mold clamping plate 20, and spanning the positions of theinjection molding station 14 and cooling and ejection station 16 isdisposed an upper mold clamping plate 22 which is for example circular.This upper mold clamping plate 22 can go up and down along four tie bars24 provided around the periphery of the injection molding station 14. Asshown in FIGS. 1, 4A and 4B, a fixing plate 26 is provided at the upperends of the tie bars 24, and this fixing plate 26 has a clampingcylinder 28 fixed thereto. The clamping cylinder 28 drives a clampingrod 28a, and this clamping rod 28a drives the upper mold clamping plate22 vertically.

As shown in FIGS. 4A and 4B, on the lower surface of the upper moldclamping plate 22 is supported rotatably a rotary wheel 30. This rotarywheel 30, as shown in FIG. 5, is fixed to a rotary shaft 34, which isdriven rotatably by a rotary actuator 32 fixed to the upper moldclamping plate 22. As shown in FIG. 2, which is a bottom view of therotary wheel 30, on the rotary wheel 30 are supported two sets ofinjection core molds 50 and neck cavity molds 60 in positionscorresponding to the stations 14 and 16. The injection core molds 50 andneck cavity molds 60 are described in detail below.

As shown in FIGS. 4A and 4B, the injection molding station 14 isprovided with a hot-runner mold 40 which is brought into nozzle contactwith the injection unit 12, and an injection cavity mold 42 is fixed tothe upper part of this hot-runner mold 40. This injection cavity mold 42has by way of example four cavities for simultaneous injection moldingat the injection molding station 14. The injection cavity mold 42 cancool injection-molded preforms by circulating a cooling medium, such aswater for a room temperature, within the cavity mold.

As shown in FIGS. 4A, 4B, 5 and 6, the two sets of injection core molds50 supported by the rotary wheel 30 each have four core pins 52, forexample, for simultaneous injection molding. As shown in FIG. 5, thebase portion 52a of each core pin 52 is supported by a core retainer 54fixed to the underside of the rotary wheel 30 and a core fixing plate 56fixed to the underside of the core retainer 54. When the clampingcylinder 28 is operated so that the clamping rod 28a drives the uppermold clamping plate 22 downward, the core pins 52 of the injection coremolds 50 are driven downward integrally with the rotary wheel 30supported by this upper mold clamping plate 22, the core retainers 54and the core fixing plates 56, and thus mold clamping is performed withrespect to the injection cavity mold 42.

Each of the two sets of neck cavity molds 60 supported by the rotarywheel 30, as shown in FIGS. 5 and 9, is constituted of a pair of splitmolds 62a and 62b, and each set of these split molds 62a and 62b isprovided in a number appropriate for simultaneous injection molding. Ineach set, a pair of split molds 62a and 62b is provided with respectivesplit plates 64a and 64b for fixing, and these split plates 64a and 64bconstitute a neck fixing plate 64. Again, as shown in FIGS. 3 to 9,above the split plates 64a and 64b is provided a neck retainer 65 whichpresses down the neck fixing plate 64. Further, guide plates 66 are alsoprovided to support the underside of the end portions of the neck fixingplate 64. The split plates 64a and 64b are maintained in the normallyclosed state by means of springs 64c shown in FIG. 2. Furthermore, thesplit plates 64a and 64b are provided with respective wedge-shapedapertures 64d, shown in FIG. 2, at their end portions. After the neckfixing plate 64 is transferred to the cooling and ejection station 16,split mold opening cams 108 described below are driven in the directionof the wedge-shaped apertures 64d drive the split plates 64a and 64balong the guide plates 66.

As shown in FIG. 7, which is an enlarged sectional diagram of section Aof FIG. 6, and FIG. 3, vertical pins 70 extend upward from the guideplates 66, with their lower ends fixed thereto, and at the upper ends ofthese vertical pins 70 are formed flanges 70a. Additionally, guide tubes72 are fixed to the core retainer 54 extending downward, and thevertical pins 70 are disposed within these guide tubes 72. A returnspring 74 is disposed between the bottom inner end of each guide tube 72and the flange 70a of the corresponding vertical pin 70. The upwardforce of these return springs 74 constantly urge the guide plates 66upward, and as a result the neck retainer 65 is always held in contactwith the core fixing plate 56.

By maintaining the contact between the core fixing plate 56 and the neckretainer 65, the mold clamping of the injection core molds 50 and neckcavity molds 60 is obtained. By means of the external force (describedbelow) applied in the cooling and ejection station 16 the urging forceof the return springs 74 is countered, and the vertical pins 70 lowered;thus the neck retainer 65 is driven downward and away from the corefixing plate 56, and the neck fixing plate 64 is pressed down. As aresult, the core pin 52 of the injection core mold 50 is separated fromthe preform 1 whose neck portion 2 is held by the neck cavity mold 60.

Next, the mechanism for the ejection of the preform from the cooling andejection station 16 is described. In this embodiment, the preformejection mechanism comprises a neck mold opening section 80 and a splitmold opening section 100. The neck mold opening section 80, as shown inFIG. 6, has a first cylinder 82, and this first cylinder 82 is fixed toa first cylinder fixing plate 84b supported from the upper mold clampingplate 22 by first pillars 84a. The first cylinder 82 drives a firstvertically moving plate 86 up and down by means of a first piston rod82a. At both ends of this first vertically moving plate 86 are providedrespective pressure drive rods 88. The upper mold clamping plate 22 hasprovided therein through-holes 22a penetrating from the upper surface tothe lower surface, and the pressure drive rods 88 are disposed withinthese through-holes 22a. In order that the initial position of the firstvertically moving plate 86 does not obstruct the rotation of the rotarywheel 30, the pressure drive rods 88 are such that their ends do notproject from the lower surface of the upper mold clamping plate 22.

As shown in FIG. 6, the rotary wheel 30, core retainer 54, and corefixing plate 56 have respective holes 30a, 54a, and 56a formed inpositions corresponding to the through-holes 22a in the upper moldclamping plate 22. Driven rods 68 are positioned within the holes 30a,54a, and 56a and fixed to the upper surface of the neck retainer 65.

When, therefore, the first cylinder 82 is driven, through the firstpiston rod 82a, the pressure drive rods 88, and the driven rods 68, theneck retainer 65 and neck fixing plate 64 are driven downward againstthe urging force of the return springs 74. As shown in FIG. 8, by thismeans each core pin 52 of the injection core molds 50 is separated fromthe preform 1 of which the neck portion 2 is held by the neck cavitymold 60. In this embodiment, it is not necessary for the core pin 52 ofthe injection core mold 50 to be completely detached from the opening ofthe preform 1, and it is sufficient if a gap opens between the core pin52 and the preform 1 into which air enters. In this embodiment, thestroke by the neck fixing plate 64, that is, the stroke by the core pins52 (the distance L in FIG. 8) for mold-opening is set to be, forexample, 50 mm.

Next the split mold opening section 100 is described. As shown in FIGS.1 and 6, this split mold opening section 100 has for example two secondcylinders 102. As shown in FIG. 9, each of these second cylinders 102 isfixed to a second cylinder fixing plate 104b supported from the firstvertically moving plate 86 by second pillars 104a. As a result, when thefirst vertically moving plate 86 is driven vertically by the firstcylinder 82, the second cylinders 102 are also driven vertically. Thesecond cylinders 102 drive second vertically moving plates 106 up anddown by means of second piston rods 102a. At both ends of these secondvertically moving plates 106 are fixed split mold opening cams 108. Thelower extremities of the split mold opening cams 108 are wedge-shaped,corresponding to the wedge-shaped apertures 64d provided in the splitplates 64a and 64b making up the neck fixing plate 64. As a result, whenthe second cylinders 102 are driven, the split mold opening cams 108 aredriven down, the wedge-shaped lower extremities are inserted into thewedge-shaped apertures 64d in the neck fixing plate 64, and thereby thesplit plates 64a and 64b are driven apart. Additionally, the respectivesplit molds 62a and 62b fixed to the split plates 64a and 64b are drivenapart, and the preform 1 is ejected from the neck cavity mold 60. Inthis preferred embodiment the drive timing of the second cylinders 102is set to be after the first cylinder 82 is driven.

Next, the operation of injection molding the preforms 1 in theembodiment above is described.

(1) Injection molding step in the injection molding station 14.

The clamping cylinder 28 is driven and the upper mold clamping plate 22is thereby driven down, whereby the injection core molds 50 and the neckcavity molds 60 are clamped to the injection cavity mold 42. After theclamped state shown in FIG. 4 is reached, by a screw inside theinjection unit 12 being advanced and rotated, the preform 1 injectionmolding material, for example polyethylene terephthalate (PET), isinjected by way of the hot runner mold 40 into the cavity defined by themolds 42, 50 and 60, and the preforms 1 are thereby injection molded.

(2) Cooling step in the injection molding station 14

The injection cavity mold 42, the injection core molds 50 and the neckcavity molds 60 each have a cooling medium, for example water at roomtemperature, circulating through them, and the resin injected into thecavity defined by the molds can be immediately cooled.

(3) Step for releasing preforms from the injection cavity mold 42 in theinjection molding station 14.

By the clamping cylinder 28 being so driven that it lifts the upper moldclamping plate 22, the injection core molds 50 and the neck cavity molds60 can be lifted up away from the injection cavity mold 42, resulting inthe open state shown in FIG. 4A. At this time, because an undercut withrespect to the mold-opening direction is formed in each of the neckportion 2 of the preforms 1, the injection-molded preforms 1 are held bythe injection core molds 50 and neck cavity molds 60 and are separatedfrom the injection cavity mold 42.

The timing at which this mold-opening starts in the injection moldingstation 14 can be made considerably earlier than a conventionalmold-opening start timing. In other words, the cooling time of thepreforms 1 in the injection molding station 14 can be shortened. This isbecause even after the preforms 1 have been released from the injectioncavity mold 42 the core pins 52 of the injection core molds 50 remaininside the preforms 1 and deformation of the preforms 1 accompanyingtheir thermal shrinkage can be prevented. Therefore, the releasetemperature for the preforms 1 in the injection molding station 14 onlyhas to be low enough for a skin layer thick enough for the shape of thepreforms 1 to be maintained after they are separated from the injectioncavity mold 42 to form at the outer surfaces of the preforms 1, and canbe higher than conventional release temperatures. Even if the releasetemperature is high in this way, because the cooling causes the preforms1 to shrink around the core pins 52 of the injection core molds 50,release from the injection cavity mold 42 can be carried out relativelysmoothly, and release problems of the preforms 1 do not occur. Also,because in the injection molding station 14 withdrawal of the core pins52 is not carried out, even if the preforms 1 are released at a highrelease temperature, the problem of the lower ends of the preforms 1being pulled up with the core pins 52 does not occur.

The clamped state of the injection core molds 50 and the neck cavitymolds 60 with respect to the preforms 1 separated from the injectioncavity mold 42 is maintained by the core fixing plate 56 and the neckretainer 65 being kept in contact with each other by the return springs74. This clamped state of the injection core molds 50 and the neckcavity molds 60 is maintained through the subsequent step oftransferring the preforms 1 until in the cooling and ejection station 16the preforms 1 are released from the injection core molds 50. Cooling ofthe preforms 1 is possible throughout the time during which this clampedstate of the injection core molds 50 and the neck cavity molds 60 ismaintained.

(4) Preform 1 transfer step

The preforms 1 are carried from the injection molding station 14 to thecooling and ejection station 16 by the rotary actuator 32 being drivenand the rotary wheel 30 being rotated thereby through 180 degrees.During this preform 1 transfer step, it is possible for cooling of thepreforms 1 by the cooling medium circulating through the injection coremolds 50 and the neck cavity molds 60 to continue without interruption.

Generally, when the preforms 1 are released from the mold at a hightemperature, crystallization occurs due to inadequate cooling and thewall surfaces of the preforms 1 become non-transparent, and particularlywhen PET is being used to make transparent containers this is a fataldefect. According to experiments carried out by the present inventors,this crystallization and loss of transparency of the preforms 1accompanying inadequate cooling is particularly marked on the innersurface of the walls of the preforms 1. This is because on the innersurface of the walls of the preforms 1 there is less surface area incontact with the mold and consequently the inner surface is more liableto be inadequately cooled than the outer surface. Also, when asconventionally the injection cavity mold 42 and the injection core molds50 are separated from the preforms 1 in the injection molding station,the inner surface of the walls is more liable to be inadequately cooledthan the outer surface because the heat-radiating surface area on theinner surface of the preforms 1 is less than of the outer surface andfurthermore heat accumulates in the interior of the preforms 1.

In this embodiment, even if in the injection molding station 14 thepreforms 1 are released from the mold at a relatively high temperature,in the subsequent transfer step it is possible for the preforms 1 tocontinue to be cooled by the injection core molds 50 and the neck cavitymolds 60. In particular, because the inner surface of the walls of thepreforms 1 can be uninterruptedly cooled by the core pins 52 of theinjection core molds 50, crystallization and loss of transparency causedby inadequate cooling can be certainly prevented. In particular, theneck portions 2, which because they are thick have large heat capacitiesand are more liable to crystallize than other portions, can be cooled bythe neck cavity molds 60 and prevented from crystallizing.

(5) Preform cooling step in the cooling and ejection station 16.

Even after the preforms 1 have been transferred to the cooling andejection station 16, by the clamped state of the injection core molds 50and the neck cavity molds 60 with respect to the preforms 1 beingmaintained, the preforms 1 can be cooled as they were during theabove-mentioned transfer step. At this time, even if in the injectionmolding station 14 the clamping cylinder 28 has been driven and theupper mold clamping plate 22 lowered for the injection molding of thenext preforms, because the above-mentioned clamped state in the coolingand ejection station 16 is maintained, cooling of the preforms 1 can becontinued.

(6) Step for separating the neck cavity molds 60 from the injection coremolds 50

Cooling of the preforms 1 by the core pins 52 of the injection coremolds 50 only has to continue long enough for crystallization caused byinadequate cooling of the inner surface of the walls of the preforms 1to be prevented and for deformation of the ejected preforms 1 to beavoided, and indeed if the preforms 1 are excessively cooled by the corepins 52, removal of the core pins 52 becomes difficult. Therefore, inthis cooling and ejection station 16, first the preforms 1 are releasedfrom the injection core molds 50. In this embodiment, this is achievedby the neck cavity molds 60 holding the preforms 1 being separated fromthe injection core molds 50.

This separation of the neck cavity molds 60 is carried out by the neckretainer 65 kept in contact with the core fixing plate 56 by the urgingforce of the return springs 74 being lowered by the neck mold openingsection 80. When the first cylinder 82 of the neck mold opening section80 is driven, the pushing force thereof transmitted through the firstpiston rod 82a, the first vertically moving plate 86, the pressure driverods 88 and the driven rods 68 causes the neck fixing plate 64 to bepressed against the neck retainer 65 and be driven downward as shown inFIGS. 3 and 8. At this time, because the preforms 1 have their neckportions 2 held by the neck cavity molds 60, the preforms 1 are alsodriven downward together with the neck fixing plate 64 and the neckcavity molds 60. Consequently, the relative separation of the neckcavity molds 60 from the injection core molds 50 results in theinjection core molds 50 being separated from the preforms 1.

This stroke through which the injection core molds 50 move with respectto the preforms 1 does not have to be so long that the core pins 52 arepulled completely clear of the open ends of the preforms 1 for thesubsequent transfer of the preforms 1 as it does conventionally, andneed only be long enough for at least gaps through which air can enterto be formed between the inner surface of the walls of the preforms 1and the core pins 52. Consequently, the mold-opening stroke of theinjection core molds 50 depends on the angle of the taper provided onthe core pins 52 and the inner surface of the walls of the preforms 1,and the greater this taper angle is, the shorter the mold-opening strokeneeds to be. Because the mold-opening stroke of the injection core molds50 can be shortened in this way, the installation height of the firstcylinder 82 can be made low and the overall height of the injectionmolding apparatus can be made low, and this is advantageous in thetransportation and installation of the apparatus.

(7) Preform ejection step

Because the preforms 1 have their neck portions 2 held by the neckcavity molds 60 comprising the pairs of split molds 62a and 62b, thepreforms 1 can be ejected by these neck cavity molds 60 being opened. Tobring this about, the second cylinders 102 of the split mold openingsection 100 are driven. This driving force of the second cylinders 102is transmitted to the split mold opening cams 108 by way of the secondpiston rods 102a and the second vertically moving plates 106. By thesplit mold opening cams 108 being driven downward, as shown in FIG. 9their ends are inserted into the wedge-shaped apertures 64d formed inthe split plates 64a and 64b, these split plates 64a and 64b are drivenopen, and the pairs of split molds 62a and 62b are thereby opened. Atthis time, even if the neck portion 2 of a preform 1 has stuck to one ofthe split molds 62a and 62b and tries to move therewith, because therespective core pin 52 of the injection core molds 50 is still insidethe preform 1, lateral movement of the preform 1 is restricted and thepreform 1 can be dropped downward without fail.

In the state before the split mold opening cams 108 are driven downward,in order to avoid the split plate opening cams 108 interfering with therotation of the rotary wheel 30 it is necessary that their ends stopwithin the thickness of the upper mold clamping plate 22. On the otherhand, because the neck fixing plate 64 which is driven open by thesesplit mold opening cams 108 is in the position most remote from therotary wheel 30, the downward stroke of the split mold opening cams 108is long. In this embodiment, because the second cylinders 102 whichdrive these split mold opening cams 108 are mounted on the firstvertically moving plate 86 driven by the first cylinder 82 and becausebefore the split mold opening cams 108 are driven the first verticallymoving plate 86 is driven, the actual downward stroke through which thesplit mold opening cams 108 are driven by the second cylinders 102 isreduced. As a result, the installation height of the second cylinders102 can be made low, the overall height of the injection moldingapparatus can be made low, and an apparatus advantageous from the pointsof view of transportation and installation can be provided.

After this preform 1 ejection step is completed, the first and secondcylinders 82 and 102 return to their original states. As a result, theneck retainer 65 is brought back into contact with the core fixing plate56 by the return springs 74, and the injection core molds 50 and theneck cavity molds 60 are returned to their clamped state in preparationfor the next injection molding.

The cooling and mold-opening steps described above carried out in thecooling and ejection station 16 only have to be finished within the timetaken for the injection molding of the next, new preforms in theinjection molding station 14 to finish, in other words within theinjection molding cycle time. The preform 1 cooling time dependsparticularly on the thickness of the main body portions of the preforms1, and the thicker the preforms 1 are the longer the cooling time thatmust be provided. In this embodiment this cooling time can be adjustedby setting the timing of the mold-opening of the injection core molds 50in the cooling and ejection station 16 as well as by adjusting thecooling time in the injection molding station 14. As a result, evenwhile the mold-release temperature in the injection molding station 14is made high and the injection molding cycle time thereby shortened,because adjustment of the cooling time is easy, a highly flexiblepreform injection molding station can be provided.

After the preform 1 injection molding in the injection molding station14 is completed, the injection core molds 50 and the neck cavity molds60 in the two stations 14 and 16 are interchanged by the rotary wheel 30being rotated through 180 degrees by the rotary actuator 32. In thisembodiment, the rotary actuator 32 comprises a reversible rotarycarrying means with a reciprocating direction of rotation for eachtransfer. As a result, even if the injection core molds 50 and the neckcavity molds 60 rotationally transferred have cooling pipes forcirculating cooling medium therethrough connected thereto, these coolingpipes will not be twisted through more than one revolution.Consequently, it is possible to connect these cooling pipes to the moldswithout using rotary connectors and their construction does not becomecomplicated.

(8) Blow-molding step

By connection of the preform injection molding apparatus to ablow-molding apparatus, the preforms 1 can be used, while stillretaining the heat of injection molding, for blow-molding of bottles orother hollow objects by the so-called hot parison method.

In this case, the preforms 1 ejected from the cooling and ejectionstation 16 are taken by a support means which holds the neck andtransferred to a blow-molding station. In the course of transfer to theblow-molding station, the temperature of the preforms 1 may be adjustedfor desired thickness distribution.

In the blow-molding station, the preforms 1 are blow-molded into bottlesby a means well known in the art. That is to say, each preform 1 isdisposed within a blow cavity mold, and is stretched biaxially by astretching rod and air blown from a blow core mold.

Because for the reasons discussed above the preforms 1 are given auniform temperature or a suitable temperature distribution, it ispossible to mold bottles of a desired thickness. Also, because whiteningcrystallization of the bottles is prevented, highly transparent bottlescan be molded. The present invention is not limited to being applied tothe hot parison blow molding method described above, and of course canalso be applied to so-called cold parison blow molding wherein thepreforms are returned to room temperature before being heated again andblow molded. In this case also, there is the effect that the injectionmolding cycle time can be shortened.

The present invention is not limited to the above-described embodiment,and various modification can be made within the scope of the invention.

In the embodiment described above, the injection core molds 50 and neckcavity molds 60 are transferred by the rotary wheel 30, but for examplein the case that the shape of the neck portion 2 does not form anundercut with respect to the mold-opening direction, the neck cavitymolds 60 are not necessarily used. In this case, after separating theinjection cavity mold 42 in the injection molding station 14, thepreforms 1 can be transferred to the cooling and ejection station 16 bythe injection core molds 50 alone. Since the preforms 1 shrink oncooling to adhere closely to the core pins 52 of the injection coremolds 50, the release from the injection cavity mold 42 can be carriedout smoothly, and even without an undercut in the neck portion 2, thepreforms 1 can be transferred by the injection core molds 50.

In the cooling and ejection station 16, to release the preforms 1 fromthe injection core molds 50, the following method may for example beused. The core pins 52 of the injection core molds 50 are provided witha function to supply compressed air into the preforms 1 for the purposesof ejection. In this case, in the cooling and ejection station 16, afterthe preforms 1 have been cooled by the injection core molds 50,compressed air is supplied from the core pins 52, and this air pressurecauses the preforms 1 to fall downward.

We claim:
 1. A method of injection molding a preform, comprising:a stepin an injection molding station of injection molding a preform inclamped molds including an injection cavity mold and injection core moldeach of which has a cooling portion; a step in said injection moldingstation of releasing said preform from said injection cavity mold; astep of transferring said preform while being cooled by said injectioncore mold to a cooling and ejection station; and a step in said coolingand ejection station of cooling said preform by said injection core moldand thereafter ejecting said preform from said injection core moldduring an injection molding cycle for a next preform in said injectionmolding station, whereinin said injection molding step, said preform,which has a neck portion having an undercut with respect to a directionof mold-opening, is injection molded using a neck cavity mold definingthe outer surface of said neck portion, and said neck cavity moldcomprises a split pair of molds having cooling portions; in saidtransfer step and said cooling step in said cooling and ejectionstation, said preform is cooled with said injection core mold and saidneck cavity mold maintained in the clamped state; and in said ejectionstep in said cooling and ejection station, said injection core mold isseparated from said neck cavity mold by relative mold-opening drivingthrough only a stroke sufficient to allow a space to open between saidinjection core mold and the inner surface of said preform held by saidneck cavity mold, and thereafter said split pair of molds of said neckcavity mold is driven to be separated, and said preform is ejected. 2.The method of injection molding a preform of claim 1, wherein:in saidpreform ejection step, said injection core mold remaining in saidpreform prevents said preform from adhering to either of said split pairof molds and moving therewith in the direction of driving said pair ofsplit molds to be separated.
 3. The method of injection molding apreform of claim 1 wherein:the cooling time of said preform is adjustedby adjusting the timing of said relative mold-opening driving in saidcooling and ejection station.
 4. The method of injection molding apreform of claim 1 wherein:said injection core mold and said neck cavitymold together are reversibly rotated between said injection station andsaid cooling and ejection station, which being separated bysubstantially 180 degrees, and said injection core mold and said neckcavity mold are transferred so as to be interchanged between saidstations.
 5. The method of injection molding a preform of claim 1wherein:in said transfer step, said neck cavity mold is held in contactwith said injection core mold by a return spring, maintaining theclamped state of both said molds; in said cooling and ejection station,said neck cavity mold holding said preform is pulled away from saidinjection core mold by an external force opposing the urging force ofsaid return spring, so that said injection core mold is separated fromsaid preform.
 6. The method of injection molding a preform of claim 1wherein:the step of separating said injection cavity mold is carried outafter the formation of a skin layer on the outer surface of said preformcooled by said injection cavity mold sufficient to maintain the shape ofsaid preform after separation from said injection cavity mold.
 7. Themethod of injection molding a preform of claim 1, wherein:in saidcooling and ejection station, said preform is ejected by blowing airfrom said injection core mold within said preform.
 8. A method ofinjection blow molding comprising:a step in an injection molding stationof injection molding a preform in clamped molds including an injectioncavity mold and injection core mold each of which has a cooling portion;a step in said injection molding station of releasing said preform fromsaid injection cavity mold; a step of transferring said preform whilebeing cooled by said injection core mold to a cooling and ejectionstation; a step in said cooling and ejection station of cooling saidpreform by said injection core mold and thereafter ejecting said preformfrom said injection core mold during an injection molding cycle for anext preform in said injection molding station, whereinin said injectionmolding step, said preform, which has a neck portion having an undercutwith respect to a direction of mold-opening, is injection molded using aneck cavity mold defining the outer surface of said neck portion, andsaid neck cavity mold comprises a split pair of molds having coolingportions; in said transfer step and said cooling step in said coolingand ejection station, said preform is cooled with said injection coremold and said neck cavity mold maintained in the clamped state; in saidejection step in said cooling and ejection station, said injection coremold is separated from said neck cavity mold by relative mold-openingdriving through only a stroke sufficient to allow a space to openbetween said injection core mold and the inner surface of said preformheld by said neck cavity mold, and thereafter said split pair of moldsof said neck cavity mold is driven to be separated, and said preform isejected; a step of transferring said preform to a blow-molding stationwhile the heat of injection molding is retained; and a step ofblow-molding a hollow body from said preform, by disposing said preformin a blow cavity mold, applying longitudinal stretching by means of astretching rod, and introducing air from a blow core mold in saidblow-molding station.
 9. Injection molding apparatus for a preformhaving an injection molding station for injection molding the preform,and a cooling and ejection station for releasing and ejecting saidpreform after cooling, said injection molding apparatuscomprising:injection core molds disposed at positions corresponding toboth of said stations, each of the injection core molds having a coolingportion for cooling said preform; an interchange transfer means forinterchanging said injection core molds between said both stations; aninjection cavity mold adapted to be clamped with said injection coremold disposed in said injection molding station, and having a coolingportion for cooling said preform; a mold clamping means operating toclamp said injection core mold and injection cavity mold in saidinjection molding station, and also operating to separate relativelysaid injection cavity mold from said preform; an ejection means,operating to eject said preform from said injection core mold after saidpreform disposed in said cooling and ejection station has been cooled bysaid injection core mold; and a neck cavity mold adapted to be clampedand opened relatively with said injection core molds and supported bysaid interchange transfer means; whereinsaid neck cavity mold comprise asplit pair of molds defining the outer surface of a neck portion of saidpreform and said split pair of molds each having cooling portions; saidinterchange transfer means transfers said preform having been injectionmolded to said cooling and ejection station while said preform is beingcooled by said neck cavity mold and said injection core mold; and saidejection means comprises:a mold opening means which operates to separatesaid neck cavity mold relative to said injection core mold through onlya stroke sufficient to allow a space to open between said injection coremold and an inner surface of said preform held by said neck cavity mold;and a split mold opening means which after said neck cavity mold hasbeen subject to said relative mold-opening operates to separate saidsplit pair of molds and eject said preform.
 10. The injection moldingapparatus for a preform of claim 9, wherein:said interchange transfermeans is a rotary wheel executing intermittent rotary transfer of saidinjection core mold between said injection molding station and coolingand ejection station, which being disposed at rotary positions separatedby substantially 180 degrees.
 11. The injection molding apparatus for apreform of claim 9, further comprising:a return spring which urges saidneck cavity mold against said injection core mold and maintains bothmolds in the clamped state; and wherein said mold opening means opposesthe urging force of said return spring and operates to separate saidneck cavity mold relative to said injection core mold.
 12. The injectionmolding apparatus for a preform of claim 11, further comprising:twosplit plates supporting respective of said split pair of moldsconstituting said neck cavity mold; a guide member guidably supportingsaid two split plates so as to be selectively contacted or separated,and to which said return spring is attached; a pressure plate disposedabove said two split plates; and a driven shaft erected in the upwarddirection above said pressure plate and of such a length that an upperend of the driven shaft does not reach said rotary wheel; and whereinsaid mold opening means comprises:a through hole provided in said rotarywheel in a position corresponding to said driven shaft; a drive shafthaving a lower end above said through hole; and a first drive meanspressingly driving said drive shaft; and by the operation of said firstdrive means, the lower end of said drive shaft, having passed throughand below said through hole in said rotary wheel, pressingly drives saiddriven shaft, and opposing the urging force of said return springoperates to separate said neck cavity mold from said injection coremold.
 13. The injection molding apparatus for a preform of claim 12,wherein:said two split plates have wedge-shaped notch portions atopposing ends; a vertically moving plate is provided which movesvertically together with said drive shaft in response to operation ofsaid first drive means; and said split mold opening means comprises:asecond drive means mounted on said vertically moving plate; and a camplate driven downward by said second drive member, and having awedge-shaped end portion which engages with said notch portions formedin said two split plates.
 14. The injection molding apparatus for apreform claim 10 wherein:said rotary wheel is driven in a reciprocatingrotary motion, and reverses the direction of rotary transfer for eachoperation.
 15. A molding apparatus for injection molding a preformhaving a neck portion and cylindrical body portion, supported by atransfer member corresponding to an injection molding station and otherstation so as to be transferred to each of said stations, comprising:aninjection core mold having a core pin which defines an inner surface ofsaid preform and cools said preform; a neck cavity mold which consistsof split molds and can be clamped with said injection core mold in amold clamping direction, said split molds defining an outer surface ofsaid neck portion and cooling said neck portion; a core fixing plate forholding said injection core mold; a neck fixing plate which consists ofsplit plates for holding said split molds of said neck cavity mold; aguide member which slidably supports said neck fixing plate in amold-opening direction of said neck cavity mold; and mold clamping meansfor clamping said neck cavity mold with said injection core mold byurging said guide member in a mold clamping direction.
 16. A moldingapparatus of claim 15, wherein said mold clamping means comprises aspring means which urges said guide member in the mold clampingdirection.
 17. A molding apparatus of claim 15, wherein said moldclamping means comprises an air cylinder which urges said guide memberin the mold clamping direction.
 18. A molding apparatus of claim 15,wherein said mold clamping means comprises a hydraulic cylinder whichurges said guide member in the mold clamping direction.
 19. A moldingapparatus for injection molding a preform having a neck portion and acylindrical body portion, provided to a transfer member corresponding toan injection molding station and other station so as to be transferredto each of said stations, comprising:an injection core mold having acore pin which defines an inner surface of said preform and cools saidpreform; a neck cavity mold which consists of split molds and can beclamped with said injection core mold in a mold clamping direction, saidsplit molds defining an outer surface of said neck portion and coolingsaid neck portion; a neck fixing plate which consists of split platesfor holding said split molds of said neck cavity mold; a first guidemember which slidably supports at least a part of an underside of saidneck fixing plate; a second guide member which slidably supports atleast a part of a top surface of said neck fixing plate; an urging meansfor urging said first guide member in the mold clamping direction; and amold-opening means which is pressed by an ejection means provided to anupper portion of said transfer means to separate said neck cavity moldfrom said injection core mold.
 20. A molding apparatus of claim 19,wherein said mold-opening means which separates said neck cavity moldfrom said injection core mold is provided to said second guide memberand comprises a driven rod extending below said transfer members.
 21. Amolding apparatus of claim 20, wherein said driven rod separates saidneck cavity mold relative to said injection cavity mold through only astroke sufficient to allow a space to open between said injection coremold and the inner surface of said preform held by said neck cavitymold.
 22. A molding apparatus of claim 19, wherein said split plateshave wedge-shaped notch portions at opposing ends.